The invention relates to a microelectronic structure having a semiconductor structure, a barrier structure, an electrode structure and a dielectric structure made of a high-epsilon material. Structures of this type are used, in particular, as part of a capacitor.
With increasing miniaturization of semiconductor circuit configurations, in particular memory cell configurations, high-epsilon materials are used as a dielectric for capacitor structures. Capacitors of this type are used, in particular, as a storage capacitor or as part of a sensor element. High-epsilon material is a term used to denote dielectric materials having a dielectric constant ∈ greater than 10. In particular, the high-epsilon materials include paraelectric and ferroelectric materials. In particular, barium strontium titanate (BST) and strontium bismuth tantilate (SBT) are being investigated with regard to their use as a storage dielectric in a storage capacitor.
High-epsilon materials are usually deposited by metal organic deposition in MOCVD (metal organic chemical vapor deposition) or MOD (metal organic deposition) processes which are carried out at high temperatures in an oxygen-containing atmosphere. In order to obtain the leakage currents of less than 10xe2x88x928 A/cm2 which are desired for memory applications, a subsequent heat treatment in oxygen is furthermore necessary, which is carried out at 550xc2x0 C. in the case of BST.
It has been proposed (see U.S. Pat. No. 5,005,102), in the context of the fabrication of capacitors in integrated circuits, to use a barrier layer made of titanium/titanium nitride in order to protect semiconductor structures configured underneath the high-epsilon material.
Investigations (see, for example, J. O. Olowolafe et al., J. Appl. Phys. Vol. 73, No. 4, 1993, pages 1764 to 1772) show that when a barrier made of titanium/titanium nitride is used, during the deposition process of the high-epsilon material, the barrier is easily oxidized and TiO2 is formed, which is an insulator and adversely affects the conductivity of the electrode structure. Moreover, titanium nitride separates at high temperatures, which can lead to the destruction of the storage capacitors.
Therefore, it has been proposed (see T. Hara et al., Jpn. J. Appl. Phys. Vol. 36 (1997), pages L893 to L895) to use as the barrier a material including three components, for example TaSiN. However, additional equipment with expensive targets is required for depositing these materials.
It is accordingly an object of the invention to provide a microelectronic structure that can form part of a storage capacitor and a method for producing the microelectronic structure which overcomes the above-mentioned disadvantageous of the prior art apparatus and methods of this general type. In particular, it is an object of the invention to provide a microelectronic structure having a semiconductor structure, a barrier structure, an electrode structure and a dielectric structure made of a high-epsilon material that can be used in producing a storage capacitor and can be fabricated without costly equipment.
With the foregoing and other objects in view there is provided, in accordance with the invention a microelectronic structure for a capacitor, which includes: a semiconductor structure; a barrier structure including a titanium layer and a titanium nitride layer; an electrode structure having a tensile mechanical layer stress; and a dielectric structure made of a high-epsilon material. The electrode structure is disposed on the barrier structure, and the dielectric structure is disposed on the electrode structure. The barrier structure, the electrode structure, and the dielectric structure form a layer stack disposed on the semiconductor structure.
The microelectronic structure has an electrode structure having a tensile mechanical layer stress. Experts also commonly use the term stress for the mechanical layer stress. The invention makes use of the insight that high-epsilon materials deposited at high temperatures have a tensile layer stress. Furthermore, the invention makes use of the insight that the layer stress of the electrode structure determines the total layer stress of electrode structure and barrier structure. By virtue of the fact that, in the structure according to the invention, the electrode structure has a tensile layer stress, that is to say the layer stress is greater than 0 Pa, and the structure curves away from the substrate at the edge of the structure, the dielectric structure and the substrate on which it is produced have a similar layer stress. This prevents a change in the layer stress as a result of the application of the dielectric structure. Such a change in the layer stress is held responsible for the separation of the electrode structure from the barrier structure in the known method and the oxidation of the barrier structure in the known method.
The dielectric structure can be formed from any desired high-epsilon material. In particular, the dielectric structure has barium strontium titanate (BST), strontium bismuth tantalate (SBT), lead zirconium titanate (PZT) or the like.
In accordance with an added feature of the invention, the electrode structure contains platinum, which is often used as an electrode material in connection with high-epsilon materials because of its reaction behavior.
In accordance with an additional feature of the invention, the electrode structure made of platinum preferably has a resistivity in the range between 10.5 and 13 xcexcxcexa9cm. It has been shown that platinum with a resistivity in this range additionally has a diffusion barrier effect for oxygen. This effect is presumably attributable to the higher density of the platinum. As a result of this diffusion barrier effect, the underlying barrier structure is additionally protected against oxidation during the deposition of the dielectric layer.
In accordance with another feature of the invention, the platinum in the electrode structure preferably has an average grain size of between 60 and 100 nm. With an average grain size in this range, platinum has a distinct [111] texture, which has proved to be advantageous for the quality of the dielectric structure deposited thereon.
In accordance with a further feature of the invention, the barrier structure is provided in such a way that it contains a titanium layer and a titanium nitride layer, since these materials are customary and have been well investigated as barrier materials in semiconductor technology. The titanium nitride layer preferably has a resistivity in the range between 70 and 200 xcexcxcexa9cm. This reduces the sheet resistance of barrier structure and electrode structure.
In accordance with a further added feature of the invention, it is particularly advantageous to provide the titanium nitride layer having a stoichiometry N:Ti greater than 1, since the oxidizability of the barrier structure is thereby reduced.
In accordance with a further additional feature of the invention, the barrier structure preferably has a layer stress  greater than xe2x88x92200 MPa resulting in that the combination of barrier structure and electrode structure has a tensile layer stress. It is particularly advantageous if the layer stress of the barrier structure is  greater than 200 MPa, since the barrier structure then also has a tensile layer stress.
In accordance with yet an added feature of the invention, the semiconductor structure preferably contains silicon and the barrier structure contains titanium nitride and titanium. The titanium layer has a thickness of between 10 and 40 nm and the titanium nitride layer has a thickness of between 80 and 200 nm. The electrode structure contains platinum and has a thickness of between 50 and 200 nm. The dielectric structure has BST and a thickness of between 8 and 50 nm.
As an alternative, the dielectric structure contains a different high-epsilon material, in particular lead zirconium titanate or strontium bismuth tantalate. In this case, the materials of the barrier structure and of the electrode structure are adapted to the material of the respective dielectric structure.
With the foregoing and other objects in view there is provided, in accordance with the invention a method of fabricating the microelectronic structure. It is advantageous to produce, on a support, a layer stack having the semiconductor structure, the barrier structure, the electrode structure and the dielectric structure. The electrode structure is formed by sputtering platinum at a sputtering temperature of at least 200xc2x0 C. It has been shown that the mechanical layer stress of the electrode structure is essentially a function of the deposition temperature. The mechanical layer stress, for which the term stress is also often used in the technical literature, is tensile when platinum is deposited by sputtering at a sputtering temperature of at least 200xc2x0 C.
In accordance with an added mode of the invention, the sputtering temperature for the deposition of the electrode structure made of platinum is preferably chosen between 450 and 550xc2x0 C. It has been shown that, at this higher deposition temperature, a lower sheet resistance of the platinum, a larger average grain size of the platinum and a pronounced [111] layer texture are additionally obtained. Furthermore, it has been observed that platinum sputtered at relatively high temperature constitutes a better diffusion barrier for oxygen and thereby protects the underlying barrier structure more effectively against oxidation during the deposition of the dielectric structure.
It has been shown that the chosen power and the pressure during sputtering have only a minor influence on the properties of the platinum of the electrode structure. The sputtering power is set in the range between 0.5 and 2 kW and the sputtering pressure in the range between 1 and 5 mTorr.
In accordance with an additional mode of the invention, the barrier layer is preferably formed from a titanium layer and a titanium nitride layer. The titanium nitride layer is formed by sputtering in an atmosphere having a nitrogen proportion of at least 70 percent. The nitrogen proportion is determined as a ratio of the gas flows in standard cubic centimeters (sccm). A gas mixture including argon and nitrogen is preferably used for the sputtering of the titanium nitride. The pressure is preferably between 5 and 15 mTorr. It has been shown that the oxidizability of the barrier structure is reduced by the high nitrogen proportion in the sputtering atmosphere.
In accordance with an another mode of the invention, the titanium nitride layer is preferably deposited at temperatures of between 400 and 500xc2x0 C. and with a nitrogen proportion of 80 percent in the sputtering atmosphere. As a result, the oxidizability of the barrier structure is reduced further. Furthermore, the mechanical layer stresses in the barrier structure become zero or slightly tensile.
In accordance with a further mode of the invention, the microelectronic structure can advantageously be used as part of a storage capacitor in a memory cell, with the electrode structure constituting a first electrode of the storage capacitor. The storage capacitor furthermore has a second electrode configured on the side of the dielectric structure which is opposite to the first electrode.
In accordance with a concomitant mode of the invention, as an alternative, the microelectronic structure can be used as part of a sensor or actuator.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a microelectronic structure, method for fabricating it and its use in a memory cell, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.